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EPIC Modeling of Soil Organic Carbon Sequestration in Croplands of Iowa

^a USDA-ARS Hydrology and Remote Sensing Lab., Bldg 007, Rm 104, BARC-West, 10300 Baltimore Avenue, Beltsville, MD 20705
^b USDA-ARS National Soil Tilth Research Lab., Room 108, 2150 Pammel Drive, Ames, IA 50011

^* Corresponding author (Hector.Causarano{at}ars.usda.gov).

Received for publication May 30, 2007. Depending on management, soil organic carbon (SOC) is a potential source or sink for atmospheric CO₂. We used the EPIC model to study impacts of soil and crop management on SOC in corn (Zea mays L.) and soybean (Glycine max L. Merr.) croplands of Iowa. The National Agricultural Statistics Service crops classification maps were used to identify corn–soybean areas. Soil properties were obtained from a combination of SSURGO and STATSGO databases. Daily weather variables were obtained from first order meteorological stations in Iowa and neighboring states. Data on crop management, fertilizer application and tillage were obtained from publicly available databases maintained by the NRCS, USDA-Economic Research Service (ERS), and Conservation Technology Information Center. The EPIC model accurately simulated state averages of crop yields during 1970–2005 (R² = 0.87). Simulated SOC explained 75% of the variation in measured SOC. With current trends in conservation tillage adoption, total stock of SOC (0–20 cm) is predicted to reach 506 Tg by 2019, representing an increase of 28 Tg with respect to 1980. In contrast, when the whole soil profile was considered, EPIC estimated a decrease of SOC stocks with time, from 1835 Tg in 1980 to 1771 Tg in 2019. Hence, soil depth considered for calculations is an important factor that needs further investigation. Soil organic C sequestration rates (0–20 cm) were estimated at 0.50 to 0.63 Mg ha^–1 yr^–1 depending on climate and soil conditions. Overall, combining land use maps with EPIC proved valid for predicting impacts of management practices on SOC. However, more data on spatial and temporal variation in SOC are needed to improve model calibration and validation.

Abbreviations: CT, conventional tillage • DMLA, maximum potential leaf area index • EPIC, Environmental Policy Integrated Climate • HI, harvest index • NT, no tillage • RT, reduced tillage • SOC, soil organic carbon • SSURGO, soil survey geographic • STATSGO, state soil geographic • WA, biomass to energy ratio • WAC2, value of CO₂ concentration and corresponding value of the parameter WA